A touch screen panel commonly includes an input device configured to receive a position information from touching the screen with a user's finger of a user. When the user's finger or an object touches a specific character or position displayed on a screen without using a keyboard, the touch screen panel including a multi-layered structure identifies the position and directly receives data from the screen to process information by an embedded software.
To recognize the touched position without degrading visibility of an image displayed on the screen, a transparent sensing electrode patterned as a predetermined shape may be used.
Examples of a transparent electrode structure widely known in the related art include a glass-ITO film-ITO film (GFF), a glass-ITO film (G1F), a glass only (G2), a glass-2 ITO films (GF2) structure.
The GFF structure has been most commonly used in the touch screen panel, and includes two transparent electrodes (indium tin oxide, ITO) configured to achieve X-axis and Y-axis configurations, and implemented as two films. In the G1F structure, a first ITO is deposited on a rear surface of glass, and a second ITO film is used in a conventional manner. In the G2 structure, an ITO thin film for the X-axis is deposited and patterned on a rear surface of a single reinforced glass, an insulation layer is formed thereon, and an ITO thin film for the Y-axis is patterned. The GF2 structure includes a single reinforces glass and an ITO film similarly to the G2 structure. In the GF2 structure, an ITO thin film for the X-axis is deposited and patterned on the ITO film, an insulation layer is formed thereon, and an ITO thin film for the Y-axis is patterned. The ITO pattern of the GF2 structure may be attached to a curved glass without generating cracks to be applied to a recent curved display such as a wearable display device.
In the G2 and GF2 structures including transparent electrode patterns implemented as X-axis and Y-axis electrodes, a bridge electrode pattern may be formed on the insulation layer for electrically connecting the transparent electrode patterns with each other. In this case, the bridge electrode and sensing patterns (X-axis and Y-axis electrodes) may be visually distinguished from each other. As a reflectance difference between the bridge electrode and the sensing patterns becomes greater, a visual difference may become clear and distinct to degrade a visibility of the display device. Particularly, in a capacitive-type touch panel, transparent electrode patterns are formed on an entire surface of a display area in the display device, and thus the transparent electrode patterns having reduced visibility may be needed.
From the aspect as mentioned above, Japanese Patent Laid-open Publication No. 2008-98169 discloses a transparent conductive film in which an under-coat layer including two layers with different refractive indexes is formed between a transparent substrate and a transparent conductive layer. In an embodiment thereof, a silicon-tin oxide layer having a high refractive index of 1.7 (with a thickness of 10 nm or more), a silicon oxide layer having a low refractive index of 1.43 (with a thickness of 30 nm), and an ITO film having a refractive index of 1.95 (with a thickness of 15 nm) as a transparent conductive layer are sequentially formed. However, the bridge electrode on the insulation layer is also clearly observed even after being attached to the display device, and an image clearance of the display device may not be sufficiently improved.